Fireflies / noise on glossy material
A few things to try when dealing with fireflies:

Enable Multiple Importance in your light:



Left is your original settings, right with Multiple importance enabled.
(click on the images to enlarge)



Using clamp indirect takes care of most of the fireflies with no noticeable side effects as far as I can see...





Now for a super clean render you might want to use Branched Path Tracing: